Gas sensor

ABSTRACT

A gas sensor, including a cylindrical outer tube; and a seal member disposed in the outer tube, the seal member including: a lead wire insert hole and an atmosphere communication hole extending in an axial direction thereof. The gas sensor further includes: a protection portion which covers the atmosphere communication hole from the rear end of the gas sensor in the axial direction, the protection portion having a protrusion which protrudes toward a rear side of the gas sensor, and has an opening smaller than an opening of the atmosphere communication hole, wherein the protrusion is disposed at a further front end side of the rear end surface of the seal member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas sensor, which holds a sensorelement for measuring a gas to be measured in a metal shell or an outertube, and has a ventilation structure for ensuring ventilation betweenthe inside and the outside of the outer tube.

2. Description of the Related Art

A gas sensor having a sensor element for detecting the concentration ofa specific gas component (e.g., oxygen) in an exhaust gas dischargedfrom an engine using a solid electrolyte body containing a ceramic suchas zirconia is well-known in the art. For example, a sensor element ofan oxygen sensor for detecting the concentration of oxygen includes adetection electrode exposed to the exhaust gas and a reference electrodeexposed to a reference gas (commonly, the atmosphere). The electrodesare formed on an outer or inner surface of the sensor element, and arepaired with a counter electrode on opposing sides of a solid electrolytebody. The sensor element detects the concentration of oxygen in theexhaust gas in accordance with the difference in partial pressure ofoxygen between two atmospheres spaced apart from the solid electrolytebody, namely between the exhaust gas and the reference gas.

This oxygen sensor includes a metal shell for holding the sensorelement, and an outer tube for covering the periphery of the sensorelement, and a seal member (grommet) may be assembled thereto to blockthe outer tube. In addition, the seal member has a lead wire insert holefor inserting a lead wire (a sensor output lead wire and a heater leadwire), and an atmosphere communication hole (or, a cylindrical hole) forintroducing the reference gas toward the reference electrode of thesensor element by ensuring ventilation between the inside and theoutside of the outer tube. Also, a filter member for introducing theatmosphere into the outer tube (air ventilation) and preventing theentry of water droplets (waterproofing properties) is provided in theatmosphere communication hole of the plug member.

In addition, as disclosed in the Patent Document 1 or 2, a gas sensorhaving a protection member for covering the atmosphere communicationhole of the seal member from a rear side (an outer side) of the outertube to protect the filter member is already known. Providing theprotection member as mentioned above prevents the filter member frombeing directly exposed to the outside and also prevents the filtermember from being damaged due to an impact from the outside, caused bycontact with plants or trees or a collision with a flying stone. Thisprotection member has a ventilation portion with a smaller opening thanthe atmosphere communication hole, and the ventilation portion cover thefilter member. Also, the protection member has a covering portion, whichis outside the line of sight and communicates with the atmospherecommunication hole from the gap with the seal member. The protectionmember is connected to the outer tube by means of an arm.

-   Patent Document 1 JP-A-2008-292459-   Patent Document 2 JP-A-2008-292460

3. Problems to be Solved by the Invention

However, among the protection members of a gas sensor disclosed in thePatent Documents 1 and 2, the protection member (see FIG. 14 of thePatent Document 2) having a plurality of small openings through theventilation unit in an axial direction has a problem in that theopenings may be clogged since each opening is too small.

Meanwhile, if a protrusion (see FIGS. 3 and 5 of Patent Document 1 andFIG. 12 of Patent Document 2) having an opening and protruding toward arear end (an outer side) with a dome shape is provided on theventilation unit, and the opening of the protrusion of the protectionmember communicates with the atmosphere communication hole by theprotection member, then the opening is not easily clogged and good airventilation can be ensured. However, if the protrusion protrudes fromthe rear end (the outer side) further than the rear end of the sealmember when the protection member having the protrusion is disposed onthe seal member to cover the filter member, a lead wire may be hooked bythe edge of the protrusion when being installed, leading to a concernthat damage to the lead wire may result.

SUMMARY OF THE INVENTION

The present invention was made to solve the above problems, and anobject thereof is to provide a gas sensor capable of preventing a leadwire from being damaged when a seal member is disposed on a ventilationunit having a protrusion to cover a filter member.

According to an illustrative aspect (1), the above object of the presentinvention has been achieved by providing a gas sensor, comprising: asensor element extending in an axial direction and having a detectionportion for detecting a gas to be detected at a front end thereof; ametal shell that surrounds a periphery of the sensor element in a radialdirection while allowing the detection portion to protrude from a frontend thereof; a cylindrical outer tube disposed at a rear side of themetal shell and having a front end fixed to the metal shell; and a sealmember disposed in the outer tube, the seal member including: a leadwire insert hole into which a lead wire for extracting a detectionsignal of the detector is inserted, the lead wire insert hole extendingin an axial direction thereof, and an atmosphere communication holeallowing atmospheric communication between an inside and an outside ofthe outer tube through a filter member having air ventilation andwaterproofing properties, the atmosphere communication hole extending inan axial direction thereof, wherein the gas sensor further includes: aprotection portion that protects the filter member by covering theatmosphere communication hole of the seal member from the rear end ofthe gas sensor in the axial direction, the protection portion having aprotrusion which protrudes toward a rear side of the gas sensor, and hasan opening smaller than an opening of the atmosphere communication hole,wherein the protrusion is disposed at a further front end side of therear end surface of the seal member.

As described above, in the gas sensor of the invention, a protrusion isdisposed at a further front end side of the rear end surface of a sealmember. In other words, since the protrusion is disposed in the sealmember, a lead wire is not hooked by the edge of the protrusion whenbeing installed. As a result, it is possible to prevent the lead wirefrom being damaged.

Also, since the protrusion is disposed in the seal member, flying stonesdo not easily collide with the protrusion, and thus the air ventilationof an opening formed in the protrusion may be favorably maintained. Inaddition, it is possible to prevent the filter member from being brokendue to external impact caused by contact with plants or trees orcollision with flying stones when a protection portion is deformed toexpose the filter member.

Also, the protrusion may have a structure protruding from the protectionportion toward the rear end side and having a smaller opening than theopening of the atmosphere communication hole. In detail, the protrusionmay protrude with a dome shape or be formed by forming two grooves inthe protection portion, and pressing a region between two grooves towardthe rear end side.

In addition, the protection portion may have a greater hardness than thefilter member. In this way, it is possible to more reliably prevent thefilter member from being broken.

In a preferred embodiment (2), the gas sensor according to (1) abovefurther comprises an arm extending from the protection portion in aradial direction, wherein the arm and the protection portion areintegrally formed with an outer tube. If the arm, the protectionportion, and the outer tube are integrally formed as mentioned above,the number of parts may be reduced.

In addition, in the gas sensor of the invention, the seal member maycrimp the outer tube toward an inner side in the radial direction sothat the seal member is held in the outer tube. Thus, in anotherpreferred embodiment (3) of the gas sensor according to (2) above, theseal member is held in the outer tube by crimping the outer tube to aninner side thereof in the radial direction. Consequently, stress causedby the crimping is applied to the seal member so that the stopperexpands toward the rear end of the gas sensor. Thus, the protrusion maybe easily disposed at a further front end side of the rear end surfaceof the seal member by using a seal member that expands toward the rearend. As a result, it is possible to easily prevent the lead wire frombeing damaged.

In yet another preferred embodiment (4) of the gas sensor according to(1) above, the gas sensor includes a protection unit having an armextending from the protection portion in a radial direction and acylindrical portion connected to the arm and covering the periphery ofthe outer tube, wherein the cylindrical portion is mechanically fixed tothe outer tube so that the protection unit is coupled to the outer tube.As mentioned above, the protection portion, the arm, and the cylindricalportion having a complex shape may be provided as a separate protectionunit independently from the outer tube, and the arm and the protectionportion may be easily coupled to the outer tube.

Also, in order to mechanically unite (fix) the cylindrical portion ofthe protection unit with the outer tube, the cylindrical portion mayhave an inner diameter smaller than the outer diameter of the outer tubeso that the cylindrical portion is press-fit into the outer tube, or thecylindrical portion may have a plurality of slits along the axialdirection so that the cylindrical portion is engaged with the outer tubeby elastic deformation.

In yet another preferred embodiment (5) of the gas sensor according to(2) above, the seal member has a groove extending outwards in a radialdirection at a rear end-facing surface of the seal member from theatmosphere communication hole while circumventing the lead wire inserthole, the groove having a cutout toward the front end of the sealmember, wherein the arm is at least partially disposed in the groove ofthe seal member.

The groove provided in the seal member promotes drainage and preventsthe deterioration of air ventilation by the atmosphere communicationhole when the seal member is wet from the outside, whereas at leastpartially disposing the arm in the groove ensures that the arm does notcollide with flying stones. In this way, it is possible to prevent thefilter member from being exposed to the outside due to movement of theprotection portion, caused by deformation of the arm. As a result, it ispossible to prevent the filter member from being broken due to externalimpact such as contact with trees or plants or collision with flyingstones.

In addition, since the arm is at least partially disposed in the grooveof the seal member, it is possible to prevent the protection portion orthe arm from rotating in a circumferential direction of the gas sensor,and it is also possible to prevent the lead wire from being damaged dueto contact with the protection portion or the arm.

Also, in a case where the arm is disposed in a part of the groove, it ispossible to prevent the protection portion or the arm from rotating in acircumferential direction of the gas sensor, or to prevent the arm frombeing deformed due to collision with flying stones. However, if the armis disposed entirely in the groove, it is possible to more reliablyprevent the protection portion or the arm from rotating in acircumferential direction of the gas sensor or to prevent the arm frombeing deformed due to a collision with flying stones.

In yet another preferred embodiment (6) of the gas sensor according to(5) above, a plurality of grooves extends outwards in the radialdirection at the rear end surface of the seal member from the atmospherecommunication hole while circumventing the lead wire insert hole, and aplurality of arms is disposed in the grooves of the seal member. Since aplurality of arms is provided, even though one arm is distorted, thedistortion is lessened due to the other arms, and thus the protectionportion may securely cover the atmosphere communication hole of the sealmember from the outside of the outer tube. In addition, in a case wherea plurality of arms is provided, circumferential rotation of theprotection portion or the arm around the gas sensor may be reliablyprevented since the arms are respectively disposed in the plurality ofgrooves. Also, it is possible to reliably prevent the lead wire frombeing damaged due to contact with the protection portion or the arm.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative aspects of the invention will be described in detail withreference to the following figures wherein:

FIG. 1 is a vertical sectional view showing a structure of the gassensor 1 according to a first embodiment;

FIG. 2 is a perspective view showing a grommet 9 before being assembled;

FIG. 3 shows the gas sensor 1, observed from a rear end in an axial Odirection (from an upper side in FIG. 1);

FIG. 4 is a perspective view showing an outer tube 3 before beingassembled;

FIG. 5 is a perspective view showing a mounting jig 400;

FIG. 6 shows the mounting jig 400, observed from a front side in amounting direction (in an arrow C direction in FIG. 5);

FIG. 7 shows the mounting jig 400, observed from a rear side in themounting direction (in an arrow D direction in FIG. 5);

FIG. 8 is a bent sectional view showing the mounting jig 400, observedin an arrow direction of the bent line E-E represented by a two-dotchain line in FIG. 5 (or FIG. 6);

FIG. 9 illustrates a holding process;

FIG. 10 illustrates a lead wire holding process;

FIG. 11 illustrates a disposing process;

FIG. 12 illustrates a shifting process;

FIG. 13 is a vertical sectional view showing a structure of the gassensor 200 according to a second embodiment;

FIG. 14 is a perspective view showing a protection member 100 accordingto the second embodiment;

FIG. 15 shows the gas sensor 200, observed from a rear side in the axialO direction (the upper side in FIG. 13); and

FIG. 16 is a partially enlarged sectional view showing a gas sensor 1,observed in an arrow direction of the bent line A-A represented by aone-dot chain line of FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a gas sensor according to an embodiment of the invention isdescribed with reference to the drawings. However, the present inventionshould not be construed as being limited thereto.

First, as an example, a structure of a gas sensor 1 according to a firstembodiment is described with reference to FIGS. 1 to 4. Also, the gassensor 1 shown in FIG. 1 is mounted to an exhaust pipe (not shown) fordischarging an exhaust gas exhausted from an engine of a vehicle or thelike. Hereinafter, in an axial O direction of the gas sensor 1, a sidedirected to a front end side of a sensor element 6 inserted into theexhaust pipe (which is a closed side and a lower side in the figure) istaken as a front end side, and a side opposite thereto (which is anupper side in the figure) is taken as a rear end side.

The gas sensor 1 shown in FIG. 1 is a sensor for detecting theconcentration of oxygen in an exhaust gas flowing in the exhaust pipe,and a cylindrical sensor element 6 having a thin and long cylindricalshape with a closed front end is held in a metal shell 5, an outer tube3, or a protector 4. Lead wires 18 for extracting a signal output fromthe sensor element 6 or connecting electric current to a heater 7mounted to the sensor element 6 are drawn from the gas sensor 1. Eachlead wire 18 is electrically connected to a sensor controller (notshown) provided apart from the gas sensor 1 or an ECU (ElectronicControl Unit) of a vehicle.

The sensor element 6 of the gas sensor 1 has a solid electrolyte body 61containing zirconia, which is formed in a lower cylinder, and areference electrode 62 made of Pt or a Pt alloy and having a porousshape is formed on an inner surface of the solid electrolyte body 61 soas to cover substantially the entire surface thereof. A front end side(or, a closed side) of the sensor element 6 is configured as a detectionportion 64, and a detection electrode 63 provided at an outer surfacethereof is exposed to the exhaust gas flowing in an exhaust pipe (notshown). Though not shown in the figure, the detection electrode 63 iscoated with a porous electrode protection layer made of a heat-resistingceramic and is protected from contamination by the exhaust gas. Also, aflange member 65 protruding outwards in a radial direction is providedat a substantially middle position of the sensor element 6 in an axial Odirection. In addition, a rod-shaped heater 7 for heating and activatingthe solid electrolyte body 61 is inserted into the cylindrical hole ofthe sensor element 6.

The sensor element 6 is surrounded by a cylindrical metal shell 5 aroundits periphery in a radial direction, and the sensor element 6 is held ina cylindrical hole 55 of the metal shell 5. The metal shell 5 is acylindrical member made of stainless steel such as SUS430, and a malescrew 52 to be screwed with an attachment portion (not shown) of theexhaust pipe is formed at a front end side of the metal shell 5. A frontend engagement portion 56 to be engaged with a protector 4, describedbelow, is formed on an outer periphery of the metal shell 5 at a furtherfront end side of the male screw 52. The detection portion 64 of thesensor element 6 protrudes at a further front end side of the front endengagement portion 56.

A tool engagement portion 53 having an enlarged diameter in a radialdirection is formed at the rear end side of the male screw 52 of themetal shell 5, and a mounting tool used for mounting the gas sensor 1 tothe attachment portion (not shown) of the exhaust pipe is engaged withthe tool engagement portion 53. A ring-shaped gasket 11 for preventinggas leakage through the attachment portion of the exhaust pipe isinserted into a portion between the tool engagement portion 53 and themale screw 52. Also, a crimping portion 57 for crimping and fixing thesensor element 6 held in the cylindrical hole 55 of the metal shell 5 isprovided at the rear side of the metal shell 5. The rear end portion 66of the sensor element 6 protrudes at the further rear end side of thecrimping portion 57. Also, a rear end engagement portion 58 to beengaged with the front end portion 31 of the outer tube 3, describedbelow, is formed on an outer periphery between the tool engagementportion 53 and the crimping portion 57.

Next, a step portion 59 having an inner periphery protruding inwards ina radial direction is provided at the front end in the cylindrical hole55 of the metal shell 5, and a cylindrical support member 13 made ofalumina is locked at the step portion 59 by means of a metallic packing12. The inner periphery of the support member 13 is also formed with astep, and the flange member 65 of the detector 6 is supported by thesupport member 13 by means of the metallic packing 14 disposed at thestepped portion. Also, a filling member 15 made of talc powder is filledin the cylindrical hole 55 at the rear end of the support member 13, anda cylindrical sleeve 16 made of alumina is disposed at the rear end ofthe filling member 15 so that the filling member 15 is positionedbetween the support member 13 and the sleeve 16.

An annular ring 17 is disposed at the rear end of the sleeve 16, and thesleeve 16 is pressed to the filling member 15 through the ring 17 sincethe crimping portion 57 of the metal shell 5 is crimped in a radialdirection. By means of the additional crimping of the crimping portion57, the filling member 15 is filled by pressure in the cylindrical hole55 of the metal shell 5 so that the flange member 65 of the sensorelement 6 is pressed toward the support member 13 locked by the stepportion 59 of the metal shell 5, and a gap is air-tightly sealed betweenthe inner peripheral surface of the cylindrical hole 55 and the outerperipheral surface of the sensor element 6. As mentioned above, thesensor element 6 is held in the cylindrical hole 55 of the metal shell 5by means of each member sandwiched between the crimping portion 57 andthe step portion 59 of the metal shell 5.

Then, the protector 4 covering the detection portion 64 of the sensorelement 6 protruding from the front end engagement portion 56 toward thefront end in the axial O direction may be assembled to the front endengagement portion 56 of the metal shell 5 by welding. The protector 4protects the detection portion 64 of the sensor element 6 protruding inan exhaust pipe (not shown) when the gas sensor 1 is mounted to theexhaust pipe from water droplets or impurities included in the exhaustgas. The protector 4 has a double structure including an outer protector41 constituting a lower cylinder and having a circumferential edge at anopen side, which is fixed to the front end engagement portion 56, and aninner protector 45 of the lower cylinder, which is fixed to the outerprotector 41. Introduction openings 42 for introducing the exhaust gasto the detection portion 64 of the sensor element 6 are respectivelyformed in the outer peripheral walls of the outer protector 41 and theinner protector 45 (where the gas introduction opening of the innerprotector 45 is not shown). Also, discharge outlets 43, 48 fordischarging water droplets or exhaust gas therein are respectivelyformed in lower walls of the outer protector 41 and the inner protector45.

In addition, a cylindrical separator 8 made of an insulating ceramic isdisposed at a further rear end side of the rear end portion 66 of thesensor element 6 in the axial O direction. The separator 8 has areceiving unit 82 that receives four connection terminals 19 (amongwhich three connection terminals 19 are shown in FIG. 1) independently.The receiving unit 82 is pressed through the separator 8 in the axial Odirection, and the separator 8 is constituted so that the front and rearends of the separator 8 may be ventilated. The connection terminals 19are respectively electrically connected to a reference electrode 62 ofthe sensor element 6, a detection electrode 63, and a pair of electrodes71 (among which one electrode 71 is shown in FIG. 1) exposed to the rearend side for electric connection to a heating resistor of the heater 7.The separator 8 receives the connection terminals 19 in a separatedstate and prevents the connection terminals 19 from contacting eachother. Core wires of four lead wires 18 (among which two lead wires 18are shown in FIG. 18) are respectively crimped and fixed to theconnection terminals 19, and each lead wire 18 is drawn out to the gassensor 1 through a grommet 9, described below. Also, a flange member 81protruding out in a radial direction is provided at the outer peripheralsurface of the separator 8, and a substantially cylindrical holdingbracket 85 is inserted into the outer peripheral surface at a furtherfront end side of the flange member 81.

In addition, the grommet 9 made of fluorine-based rubber is disposed atthe rear end side of the separator 8. As shown in FIG. 2, the grommet 9is a member formed in a substantially cylindrical shape with the axial Odirection being in a height direction, and the grommet 9 has anatmosphere communication hole 91 and four lead wire insert holes 92,passing through in the axial O direction. The atmosphere communicationhole 91 is formed at the center of the grommet 9 in a radial direction,and the lead wire insert holes 92 are respectively formed at regularintervals in a peripheral direction around the atmosphere communicationhole 91 at a further outer end side of the atmosphere communication hole91. The atmosphere communication hole 91 is further provided tointroduce the atmosphere into the gas sensor 1 (or, into the outer tube3, described below) through the receiving unit 82 of the separator 8, asshown in FIG. 1. In the outer tube 3, the sensor element 6 is fixed tothe metal shell 5 while its rear end portion 66 is protruding, but thereference electrode 62 formed in the bottom-provided tube of the sensorelement 6 may be exposed to the atmosphere. Also, as shown in FIG. 3,the four lead wires 18 are independently inserted into the four leadwire insert holes 92, respectively. Also, the grommet 9 corresponds tothe “seal member” of the invention.

In addition, as shown in FIGS. 2 and 3, four grooves 93 extending with agroove shape along a radial direction toward the outer periphery fromthe location of the atmosphere communication hole 91 are formed in arear end-facing surface 99 of the grommet 9, which is oriented toward arear end side when the grommet 9 is assembled to the gas sensor 1. Thegroove 93 has a cutout toward the front end of the grommet 9 and has abottom surface 94 and two side surfaces 95 connecting the bottom surface94 with the rear end-facing surface 99. Each groove 93 is disposedbetween two adjacent lead wire insert holes 92 so as to circumvent thelocations of four lead wire insert holes 92 opening on the rearend-facing surface 99. Thus, the rear end-facing surface 99 is dividedinto 4 sections by means of the grooves 93.

As shown in FIG. 1, a filter member 87 and its fastener bracket 88 areinserted into the atmosphere communication hole 91 of the grommet 9. Thefilter member 87 is for example a thin film-type filter having amicron-sized mesh structure made of a fluorine resin such as PTFE(polytetrafluoroethylene), and the filter member 87 allows passage ofthe atmosphere while not allowing the passage of water droplets. Also,the fastener bracket 88 is a cylindrical member and is fixed to thegrommet 9 with the filter member 87 being interposed between the outerperiphery of the fastener bracket 88 and the inner periphery of theatmosphere communication hole 91. The grooves 93 of the grommet 9 formchannels so that water droplets, which can not pass through the filtermember 87, flow toward the outer periphery and do not remain on thefilter member 87. For this reason, the rear end of the filter member 87may be disposed at the further rear end side of the bottom surface 94 ofthe groove 93. Also, the groove 93 may have an inclination oriented fromthe front end side to the rear side in the axial O direction as itapproaches the central side from the outer side in a radial direction.

Then, the cylindrical outer tube 3 extending in the axial O directionmay be assembled at the rear end side of the metal shell 5. As shown inFIG. 4, the outer tube 3 is made by processing stainless steel such asSUS304 into a cylindrical shape extending along the axial O direction,and then processing a front end portion 31 located at a front side (alower side in FIG. 4) into a relatively greater diameter than the otherportion of the outer tube 3. The inner diameter of the front end portion31 is greater than the outer diameter of the rear end engagement portion58 so that the front end portion 31 is engaged with the rear endengagement portion 58 (see FIG. 1) of the metal shell 5. Also, as shownin FIGS. 3 and 4, a rear end of the rear end portion 38 located at arear end side of the outer tube 3 is bent inwards in a radial directionto form a connection portion 32, and four arms 33 having a plate shapeextending in the axial O direction protrude from four locations in thecircumferential direction of the connection portion 32.

In addition, each arm 33 is respectively connected to the outerperiphery of a disk-shaped protection portion 34. The outer diameter ofthe protection portion 34 is substantially identical to that of theatmosphere communication hole 91 of the grommet 9, shown in FIG. 2, andthe protection portion 34 is supported by the arm 33 as the protectionportion 34 covers the atmosphere communication hole 91 so that itsthickness direction is in agreement with the axial O direction, as shownin FIGS. 1 and 3. Also, as shown in FIG. 4, a protrusion 35 protrudingtoward the rear end of the protection portion 34 is formed. The openingprovided in the protrusion 35 is smaller than the opening (size) of theatmosphere communication hole 91 (see FIG. 1), thereby preventing theingression of flying stones or the like into the atmospherecommunication hole 91. Also, the opening of the protrusion 35 ensuresair ventilation between the outside and the atmosphere communicationhole 91 (or, air ventilation between the inside and the outside of theouter tube 3). As the protection portion 34 is provided as describedabove, the filter member 87 disposed in the atmosphere communicationhole 91 may be protected against external impact such as contact withplants or trees and collision with flying stones, and thus it ispossible to prevent the filter member 87 from being broken.

The outer tube 3 configured as above is disposed at the rear end of themetal shell 5 while surrounding the side surfaces of the rear endportion 66 of the detector 6, the separator 8 and the grommet 9 alignedin the axial O direction, as shown in FIG. 1. The front end portion 31of the outer tube 3 is fitted in the outer periphery of the rear endengagement portion 58 of the metal shell 5, and the outer tube 3 iscrimped inwards in a radial direction from the outer periphery. Also,the outer tube 3 is fixed to the metal shell 5 by performing laserwelding around the entire outer periphery of the front end portion 31.

In addition, the side surface of the outer tube 3 corresponding to alocation at a further front end side of the flange unit 81 of theseparator 8 is crimped inwards in a radial direction around the entireouter periphery thereof. The holding bracket 85 is disposed at thislocation, and the holding bracket 85 is crimped and held in the outertube 3 while holding the separator 8 therein. Also, the side of theouter tube 3 corresponding to a location at a further rear end side ofthe flange unit 81 of the separator 8 is also crimped inwards in aradial direction at several locations in a peripheral direction. Theadditional crimping at the above region is performed at a locationcontacting the rear end of the flange member 81, and thus the flangemember 81 is interposed between the crimped region and the holdingbracket 85, thereby controlling the movement of the separator 8 in theaxial O direction.

Also, if the outer tube 3 is fixed to the metal shell 5, as shown inFIG. 1, the protrusion 35 provided on the outer tube 3 is disposed at afurther front end side of the rear end surface 99 of the grommet 9. Inother words, the protrusion 35 is disposed in the grommet 9. In thisway, the lead wire 18 is not hooked by the edge of the protrusion 35when being installed. As a result, it is possible to prevent the leadwire 18 from being damaged.

In addition, since the protrusion 35 is disposed in the grommet 9,flying stones do not easily collide with the protrusion 35, and thus theopening formed in the protrusion 35 may favorably maintain airventilation. In addition, it is possible to prevent the filter member 87from being broken due to external impact such as contact with trees orplants or collision with flying stones when the protection portion 34 isdeformed to expose the filter member 87.

Also, since the arm 33 and the protection portion 34 are formedintegrally with the outer tube 3, the number of parts may be reduced.

In addition, as shown in FIG. 1, the rear end portion 38 of the outertube 3 surrounding the outer periphery of the grommet 9 is crimpedinwards in the radial direction from the outer periphery, and thegrommet 9 is fixed to the outer tube 3. Since the outer tube 3 iscrimped inwards in the radial direction as mentioned above, in aconfiguration where the grommet 9 is held in the outer tube 3, thegrommet 9 expands at the rear end of the gas sensor 1 since the stresscaused by the crimping is applied to the grommet 9. Thus, the protrusion35 may be more easily disposed at a further front end side of the rearend surface 99 of the grommet 9 by using the expansion of the grommet 9at the rear end. As a result, it is possible to easily prevent the leadwire 18 from being damaged.

Also, as shown in FIG. 1, while the arms 33 are disposed in the rear endportion 38 of the outer tube 3 and the grommet 9 disposed at the rearside of the separator 8, the rear end surface 99 of the grommet 9divided into four sections protrudes toward the rear end from the outertube 3 except for the regions between the four arms 33, and the arms 33are disposed in the grooves 93 as shown in FIG. 3. Since the arms 33 aredisposed in the grooves 93, flying stones do not easily collide with thearms 33. In this way, it is possible to prevent the filter member 87from being exposed to the outside due to the movement of the protectionportion 34, caused by deformation of the arm 33. As a result, it ispossible to prevent the filter member 87 from being broken due toexternal impact such as contact with trees or plants or collision withflying stones.

In addition, since the arm 33 may be disposed in the groove 93 of thegrommet 9, it is possible to prevent the protection portion 34 or thearm 33 from rotating in a circumferential direction of the gas sensor 1,and it is also possible to prevent the lead wire 18 from being damageddue to contact with the protection portion 34 or the arm 33.

Also, as shown in FIG. 1, the arm 33 is disposed while forming a gap T1with the bottom surface 94 of the groove 93. In this way, even thoughthe grommet 9 thermally expands due to the heat received from theexhaust pipe or the exhaust gas or expands at the rear side of the gassensor 1, the groove 93 of the grommet 9 is not hooked by the arm 33. Asa result, the groove 93 of the grommet 9 does not expand with adifferent ratio from other regions (for example, the four regions thatconstitute the rear end surface 99), and it is possible to suppress thegeneration of cracks in the groove 93 of the grommet 9.

Also, since a plurality of arms 33 is used, even though one arm 33 isdistorted, the other arms 33 lessen the distortion, and thus theprotection portion 34 may securely cover the atmosphere communicationhole 91 of the grommet 9 from the rear side of the outer tube 3. Inaddition, in the case where a plurality of arms 33 is used, since thearms 33 are respectively disposed in the plurality of grooves 93provided in the grommet 9, it is possible to reliably prevent theprotection portion 34 or the arms 33 from rotating in a circumferentialdirection of the gas sensor 1, and it is also possible to prevent thelead wire 18 from being damaged due to contact with the protectionportion 34 or the arm 33.

Next, one example of a method for producing the gas sensor 1 isdescribed in the following sequence.

First, the structure of a mounting jig 400 used for producing the gassensor 1 will be described with reference to FIGS. 5 to 8. FIG. 5 is aperspective view showing the mounting jig 400. FIG. 6 shows the mountingjig 400, observed from a front side in the mounting direction (in anarrow C direction in FIG. 5). FIG. 7 shows the mounting jig 400,observed from a rear side in the mounting direction (in an arrow Ddirection in FIG. 5). FIG. 8 is a sectional view showing a bend of themounting jig 400, observed in an arrow direction of the bent line E-Erepresented by a two-dot chain line in FIG. 5 (or FIG. 6).

The mounting jig 400 shown in FIG. 5 is a jig for disposing the outertube 3 when assembling the gas sensor 1 (see FIG. 1), and for example,the mounting jig 400 is made of NBR (nitrile rubber) and has acylindrical shape with a central axis P (represented by a one-dot chainline in the figure) in the mounting direction. As shown in FIGS. 5 to 8,the mounting jig 400 has a base 420 in which diameter is enlarged in therear side of the mounting direction and has a stepped shape, and aholding unit 410 is formed so as to protrude from the base 420 towardthe front side in the mounting direction. The holding unit 410 is usedfor holding the outer tube 3 integrally with the mounting jig 400, andin detail, four protrusions 411 capable of being inserted into the gap(see FIG. 4) surrounded by the protection portion 34, the arm 33, andthe rear end portion 38 of the outer tube 3 are arranged in a row in acircumferential direction. When the outer tube 3 is held, the arm 33 isinserted between sides 412 of adjacent two protrusions 411 in thecircumferential direction of the central axis P.

Also, the inner side 413 toward the central axis P of each protrusion411 surrounds the central axis P to form a passage into which theprotection portion 34 is inserted. At this time, the passage has aninner diameter slightly smaller than the outer diameter of theprotection portion 34 so that a load is applied to the protectionportion 34. Also, as shown in FIG. 8, the passage formed by the innerside 413 is enlarged near a root of the base 420 of the holding unit410, and, if the protection portion 34 moves to that position, theprotection portion 34 is released from the load applied from each innerside 413. At this time, in order to prevent contact between theprotection portion 34 and the base 420, a concave receiving unit 421 incommunication with the passage formed by the inner side 413 of theprotrusion 411 is formed in the base 420. Also, the outer side 414 ofthe protrusion 411 is arranged at a location forming a gap with the rearend portion 38 of the outer tube 3. However, even though the protrusion411 of the holding unit 410 respectively protrudes from the base 420,the protruding length of the protrusion 411 from the base 420 isadjusted so that the outer tube 3 does not come into contact with thebottom surface 94 of the groove 93 of the grommet 9. This is at a timewhen the front end surface 415 of the outer tube holding unit 410 in themounting direction contacts the rear end-facing surface 99 of thegrommet 9, during the producing process of the gas sensor 1, describedbelow. In other words, when the outer tube 3 is held in the mounting jig400, the front end surface 415 of the protrusion 411 is disposed atleast at a further front end side of the arm 33 in the mountingdirection.

In addition, as shown in FIGS. 5 to 8, four lead wire holding units 430having a groove shape through the rear end surface of the base 420 inthe mounting direction from the front end surface of the holding unit410 in the mounting direction along the central axis P are formed in theouter peripheral surface of the mounting jig 400. The lead wire holdingunit 430 includes a bottom wall 431 having a circular cross-section andprovided at a center location in the section of each protrusion 411 withrespect to the central axis P of the holding unit 410, and side walls432 facing each other with a width narrower than the inner diameter ofthe bottom wall 431 (the diameter of its cross-section). The innerdiameter of the bottom wall 431 is substantially identical to the outerdiameter of the lead wire 18 (see FIG. 1) of the gas sensor 1. Eventhough the lead wire 18 is disposed in the bottom wall 431 when the leadwire 18 is inserted into the lead wire holding unit 430, the side walls432 prevent the lead wire 18 from being separated since the side wall432 has a width narrower than the outer diameter of the lead wire 18. Inaddition, the arrangement of the central axes P of the four bottom walls431 with respect to the cross-section orthogonal to the central axes Pis substantially identical to the arrangement of the axes O of the fourlead wire insert holes 92 with respect to the cross-section orthogonalto the axes O of the grommet 9. In this way, the lead wire insert hole92 of the grommet 9 is connected to the bottom wall 431 of the mountingjig 400 when the front end surface 415 of the outer tube holding unit410 in the mounting direction comes in contact with the rear end-facingsurface 99 of the grommet 9. Also, the outer diameter of the base 420 isformed to be deeper than the outer diameter of the outer surface 414 ofthe protrusion 411. For this reason, the depth of the groove of the leadwire holding unit 430 in the base 420 is greater than the depth of thegroove in the holding unit 410, and the side wall 432 more securelyprevents separation of the lead wire 13 from the base 420.

Next, the method for producing the gas sensor 1 using the mounting jig400 will be described with reference to FIGS. 9 to 12. FIG. 9illustrates the holding process. FIG. 10 illustrates the lead wireholding process. FIG. 11 illustrates the arranging process. FIG. 12illustrates the shifting process. Also, the sectional views of the gassensor 1 or the mounting jig 400 in FIGS. 9 to 12 are based on the caseof being viewed in an arrow direction in the bent line Z represented bya dotted line in FIG. 3. Hereinafter, the process of mounting the outertube 3 to the grommet 9 is described, but the other producing processesin relation to the gas sensor 1 are already well-known and thus will notbe described in detail here.

The metal shell 5 of the gas sensor 1 shown in FIG. 1 is produced byforging a rod-shaped steel made of stainless steel such as SUS430, thencutting the steel to form a tool engagement portion 53 or a rear endengagement portion 58, a male screw 52, a cylindrical hole 55, and thelike, and then performing rolling to form a thread at the male screw 52.Also, the sensor element 6 is produced by forming a reference electrode62 or a detection electrode 63 by means of, for example, plating on thesurface of a solid electrolyte body 61 formed in a lower cylinder, thenforming an electrode protection layer by covering the surface of thedetection electrode 63, and then firing the electrode protection layer.In addition, a protector 4 produced separately is adhered to the metalshell 5 by welding, and the sensor element 6 is crimped and held in thecylindrical hole 55 of the metal shell 5, thereby producing anintermediary body of the front end of the gas sensor 1.

Meanwhile, core wires of lead wires 18 of four connection terminals 19made of conductive plates are adhered by additional crimping, amongwhich two connection terminals 19 are connected to the electrode 71 ofthe heater 7. Along with receiving the connection terminals 19 and theheater 7 in the separator 8, the lead wires 18 are inserted into theseparator 8 and the grommet 9. Also, the filter member 87 and thefastener bracket 88 are inserted into the atmosphere communication hole91 of the grommet 9.

[Holding Process]

Then, as shown in FIG. 9, the four lead wires 18 drawn from the leadwire insert hole 92 of the grommet 9 are respectively inserted into gaps(see FIG. 4) surrounded by the protection portion 34, the arms 33, andthe rear end portion 38 of the outer tube 3 so that the lead wires 18 donot contact the arms 33 or the protection portion 34. In this state, thefront side of the mounting jig 400 in the mounting direction is arrangedtoward the outer tube 3 so that the central axis P is arranged inagreement with the axis O of the outer tube 3. Also, each protrusion 411of the holding unit 410 is inserted into each gap surrounded by theprotection portion 34, the arm 33, and the rear end portion 38 of theouter tube 3. In other words, the arm 33 is placed between the sides 412of adjacent protrusions 411 in the circumferential direction withrespect to the central axis P, and the protection portion 34 isrespectively disposed between the inner sides 413 of four protrusions411, which face the central axis P. In this connection, the mounting jig400 and the outer tube 3 are positioned with respect to each other.Also, if the mounting jig 400 is moved in the mounting direction alongthe axis O as is and the protection unit 34 of the outer tube 3 isreceived in the receiving unit 421 of the mounting jig 400, the innerside 413 prevents the protection portion 34 from being separated (seeFIG. 10), and the outer tube 3 is held integrally with the mounting jig400.

[Lead Wire Holding Process]

Then, as shown in FIG. 10, four lead wires 18 are respectively insertedinto a gap between adjacent side walls 432 of the lead wire holding unit430 provided to the protrusions 411 of the mounting jig 400, anddisposed to be held in a bottom wall 431. The lead wire 18 prevents eachside wall 432 having a smaller width than the outer diameter thereoffrom being separated, and each lead wire 18 is disposed to be held inthe bottom wall 431. Thus, the lead wire 18 is surrounded by theprotrusion 411 and protected against contact with the protection portion34, the arm 33, and the rear end portion 38 of the outer tube 3.

[Disposing Process]

As described above, the mounting jig 400 is made of NBR, and thus themounting jig 400 allows the lead wire 18 to slide thereon while holdingthe lead wire 18 in the bottom wall 431 of the lead wire holding unit430. As shown in FIG. 11, if the outer tube 3 integrally held to themounting jig 400 is slid in an extension direction of the lead wire 18,the mounting jig 400 and the outer tube 3 are guided by the lead wire 18and reach the rear end side of the grommet 9. Since the outer tube 3 andthe lead wire 18 are positioned with respect to each other so that thelead wire 18 does not contact the outer tube 3 due to the mounting jig400, the outer tube 3 does not graze or damage the lead wire 18 whilesliding.

When the mounting jig 400 and the outer tube 3 reach the rear end sideof the grommet 9, the front end surface 415 of the mounting jig 400comes into contact with the rear end-facing surface 99 of the grommet 9due to the protruded length of the protrusion 411 from the base 420before the arm 33 of the outer tube 3 contacts the bottom 94 of thegroove 93 of the grommet 9. At this time, the bottom wall 431 of thelead wire holding unit 430 of the mounting jig 400 is disposed inconnection with the lead wire insert hole 92 of the grommet 9 by theguidance of the lead wire 18. Since the mounting jig 400 is positionedwith respect to the grommet 9 in this way, the region between the sides412 of the protrusions 411 is connected to each groove 93 of the grommet9, and the passage formed in the inner side 413 is connected to theatmosphere communication hole 91 of the grommet 9.

[Shifting Process]

Also, as shown in FIG. 12, the outer tube 3 is pressed in the mountingdirection along the axis O. The protection portion 34 of the outer tube3 is guided toward the atmosphere communication hole 91 of the grommet 9by the inner side 413 of the protrusion 411 of the mounting jig 400, andthe arm 33 is guided between the sides 412 of the protrusions 411 towardeach groove 93 of the grommet 9. In addition, the arm 33 is received ineach groove 93 of the grommet 9, and the protection portion 34 isdisposed in a region extending from the inner periphery of theatmosphere communication hole 91 in the axial O direction at the rearend of the filter member 87 to block the atmosphere communication hole91. At this time, the flange member 81 of the separator 8 is engagedwith the outer tube 3 so that the arm 33 does not come into contact withthe bottom surface 94 of the groove 93, but the arm 33 is disposed withthe gap S from the bottom surface 94 of the groove 93. Also, the gap Shas a length greater than the gap T1. Since the grommet 9 is fixed bythe outer tube 3 due to the additional crimping in a subsequent process,the above dimension is set while considering the fact that the grommet 9expands to the rear end.

Since the mounting jig 400 contacts the grommet 9 before the outer tube3 contacts the bottom surface 94 of the groove 93 as described above, apassage for guiding the arm 33 or the protection portion 34 to thegroove 93 or the atmosphere communication hole 91 respectively isformed, and then the outer tube 3 is engaged with the grommet 9. At thistime, as the protection portion 34 is separated from the filter member87, the arm 33 is pressed so that the arm 33 of the outer tube 3 isdisposed in the groove 93 of the grommet 9. In this way, as shown inFIG. 12, when the filter member 87 is assembled to the grommet 9, eventhough the filter member 87 is exposed at a further rear end side of thegroove 93, it is possible to prevent the protection portion 34 of theouter tube 3 from contacting the grommet 9 and to also prevent thefilter member 87 from being broken when grommet 9 is fitted into theouter tube 3.

In addition, since the separator 8 and the grommet 9 are not assembledto the outer tube 3 while the arm 33 presses the bottom surface 94 ofthe groove 93, it is possible to prevent the generation of cracks in thegroove 93 of the grommet 9, which occurs when the groove 93 of thegrommet 9 shrinks due to the arm 33. Furthermore, the ratio of shrinkageat the groove 93 of the grommet 9 is different from other regions of thegrommet 9 (for example, the four regions that constitute the rearend-facing surface 99).

In the following process, the mounting jig 400 is removed, and theholding bracket 85 is inserted between the outer tube 3 and theseparator 8 to crimp the outer tube 3 so that the separator 8 is held tothe outer tube 3. Also, the rear end portion 38 of the outer tube 3 iscrimped to fix the grommet 9 to the outer tube 3, also the front endportion 31 of the outer tube 3 is engaged with the rear end engagementportion 58 of the metal shell 5, and the region around the front endportion 31 is crimped and laser-welded, thereby producing the gas sensor1.

Next, an example of a gas sensor 200 according to a second embodiment ofthe invention is described with reference to FIGS. 13 to 16. FIG. 13 isa vertical sectional view showing a structure of the gas sensor 200according to the second embodiment. FIG. 14 is a perspective viewshowing a protection member 100 according to the second embodiment. FIG.15 shows the gas sensor 200, observed from the rear side (the upper sidein FIG. 1) in the axial O direction. FIG. 16 is a partially enlargedsectional view showing the rear end of the gas sensor 200, observed fromthe arrow direction in the bent line A-A represented by the one-dottedchain line of FIG. 15.

Also, the gas sensor 200 of the second embodiment does not include theprotection portion 34 and the arm 33 provided to the outer tube 3 as thegas sensor 1 of the first embodiment, but as shown in FIG. 14, theprotection unit 100 having a protection portion 110 and an arm 120 ismechanically adhered to an outer tube 103. In addition, the componentsof the gas sensor 200 other than the protection unit 100 and the outertube 103 are identical to those of the gas sensor 1. Thus, the outertube 103 and the protection unit 100 are described here, and the othercomponents are not described or simply described.

As shown in FIG. 13, a front end portion 131 of a cylindrical outer tube103 made of stainless steel such as SUS304 is engaged to the rear endengagement portion 58 of the metal shell 5. The front end portion 131 iscrimped from the outer periphery and adhered to the rear end engagementportion 58 by further performing laser welding around the outerperiphery. The outer tube 103 extends toward the rear end along theaxial O direction, and surrounds the outer periphery of the rear endportion 66 of the sensor element 6 or the separator 8, which is disposedat a further rear end side, in a radial direction. The outer peripheryof the outer tube 103 corresponding to the disposed location of theseparator 8 is crimped in a radial direction, and for this reason, theholding bracket 85 is crimped and held in the outer tube 103 whileholding the separator 8 therein.

In addition, the grommet 9 made of fluorine-based rubber is fitted intoan opening 132 at the rear end of the outer tube 103. The grommet 9 isfixed to the outer tube 103 since the grommet 9 is crimped to the innerside in a radial direction from the outer periphery of the rear endportion 138 of the outer tube 103. In addition, a crimping portion 135formed by the additional crimping forms a groove shape surrounding theouter periphery of the outer tube 103 in a radial direction with aconcave state.

Then, the protection unit 100 for covering the atmosphere communicationhole 91 of the grommet 9 and preventing the filter member 87 from beingdamaged due to external impact such as contact with trees or plants orcollision with flying stones may be assembled to the rear end of theouter tube 103. The protection unit 100 is produced by pressing astainless steel sheet such as SUS into a cap shape as shown in FIG. 14.

The protection unit 100 has a protection portion 110 produced byprocessing a metal plate into a circular shape, and two carving (dented)portions 115 having openings 116 through the metal plate are formed bydepressing the metal plate from the bottom side (the lower side in FIG.14) in the thickness direction by pressure. Four arms 120 having a plateshape extending outwards in four radial directions are formed around theprotection portion 110.

Also, the ends of the arms 120 opposite the protection portion 110 areconnected with each other in a circumferential direction by an annularconnection unit 140. In addition, the outer periphery of the connectionunit 140 extends in the thickness direction of the protection portion110 to form a cylindrical portion 150 having a cylindrical shape. Thecylindrical portion 150 has an inner diameter slightly greater than theouter diameter of the rear end portion 138 of the outer tube 103, andthe length of the cylindrical portion 150 in the thickness direction isset so that the cylindrical portion 150 extends further at the rear endof the outer tube 103 toward the front end side than the crimpingportion 135. Also, a U-shaped cut portion 155, having a front end in thethickness direction that is connected to the cylindrical portion 150 andhaving a rear end in the thickness direction that is depressed, isprovided to the cylindrical portion 150. Six cut portions 155 areprovided at substantially regular intervals in the circumferentialdirection of the cylindrical portion 150 (six cut portions are just oneexample, and the number of cut portion may be at least one). Inaddition, a protruded portion 158 formed by depressing the cylindricalportion 150 to protrude inwards is provided at the front end of thecylindrical portion 150 in the thickness direction. Three protrudedportions 158 are provided at substantially regular intervals in thecircumferential direction without overlapping the cut portions 155 (FIG.3 shows two protruded portions). Also, the number of the protrudedportions 158 is three as an example, and the number of the protrudedportions 158 is preferably at least three, considering that movement ofthe protection unit 100 should be controlled to the minimum when theprotection unit 100 is mounted to the outer tube 103.

As shown in FIGS. 15 and 16, the protection unit 100 configured as aboveis mounted on the gas sensor 200 by covering the outer tube 103 with thecylindrical portion 150 from the front side in the thickness directionto the rear end 138 of the outer tube 103, disposing the protectionportion 110 from the rear end of the filter member 87 to the rear end ofthe atmosphere communication hole 91, and blocking the atmospherecommunication hole 91 with the protection portion 110. At this time, thearms 120 of the protection unit 100 are disposed in the grooves 93 ofthe grommet 9, respectively, and the cylindrical portion 150 is arrangedto surround the outer periphery of the rear end 138 of the outer tube103. The protruded portions 158 of the cylindrical portion 150 come intocontact with the outer periphery of the outer tube 103, where thecrimping portion 135 is not formed, and the cylindrical portion 150 ispositioned in the radial direction with respect to the outer tube 103 bymeans of the protruded portions 158. In addition, each cut portion 155of the cylindrical portion 150 contacts the wall in the groove-typeconcave portion formed by the crimping portion 135 of the outer tube103.

In addition, in the protection unit 100, the cylindrical portion 150 isfitted at the rear end of the outer tube 103 from the outside thereof,and the cut portion 155 is supported by the crimping portion 135. Atthis time, since the cut portion 155 of the protection unit 100 haselasticity, the cut portion 155 may remain engaged with the crimpingportion 135 of the outer tube 103 by elastic deformation. Also, sincethe cylindrical portion 150 is positioned in the radial direction bymeans of the protruded portion 158, the protection unit 100 may besecurely and mechanically fixed to the rear end of the outer tube 103without movement. In this connection, the protection portion 110disposed at the rear side of the atmosphere communication hole 91 at arear end of the filter member 87 disposed in the atmospherecommunication hole 91 may maintain protection of the filter member 87even though an external impact such as contact with trees or plants andcollision with flying stones is applied thereto, and also the protectionportion 110 may reliably prevent the filter member 87 from being broken.Meanwhile, even though the protection portion 110 covers the atmospherecommunication hole 91, the air ventilation of the atmospherecommunication hole 91 may be ensured through the protection portion 110since the opening 116 is formed in the carving portion 115 of theprotection portion 110.

Also, if the protection unit 100 is fixed to the outer tube 3, as shownin FIG. 16, the carving portion 115 provided on the protection portion110 is disposed at a further front end side of the rear end surface 99of the grommet 9. In other words, the carving portion 115 is disposed inthe grommet 9. In this way, the lead wire 18 is not hooked by the edgeof the dented portion 115 when being installed. As a result, it ispossible to prevent the lead wire 18 from being damaged.

In addition, since the carving portion 115 is disposed in the grommet 9,flying stones do not easily collide with the carving portion 115, andthus the opening 116 formed in the dented portion 115 may favorablymaintain air ventilation. In addition, it is possible to prevent thefilter member 87 from being broken due to external impact such ascontact with trees or plants or collision with flying stones when theprotection portion 110 is deformed to expose the filter member 87 to theoutside.

Also, since the protection portion 110, the arm 120, and the cylindricalportion 150 having a complex shape are provided as a separate protectionunit 100 independently from the outer tube 103, the arm 120 and theprotection portion 110 may be easily coupled to the outer tube 103.

In addition, as shown in FIG. 13, while the arms 120 are disposed in therear end 138 of the outer tube 103 and the grommet 9 is disposed at therear end side of the separator 8, the rear end surface 99 of the grommet9 divided into four sections protrudes toward the rear end from theouter tube 103 except for the regions between the four arms 120, and thearms 120 are disposed in the grooves 93 as shown in FIG. 15. Since thearms 120 are disposed in the grooves 93, flying stones do not easilycollide with the arms 120. In this way, it is possible to prevent thefilter member 87 from being exposed to the outside due to the movementof the protection portion 110, caused by the deformation of the arm 120.As a result, it is possible to prevent the filter member 87 from beingbroken due to external impact such as contact with trees or plants orcollision with flying stones.

In addition, since the arm 120 may be disposed in the groove 93 of thegrommet 9, it is possible to prevent the protection portion 110 or thearm 120 from rotating in a circumferential direction of the gas sensor200. It is also possible to prevent the lead wire 18 from being damageddue to contact with the protection portion 110 or the arm 120.

Also, as shown in FIG. 16, the arm 120 is disposed while forming a gapT2 with the bottom surface 94 of the groove 93. In this way, even thoughthe grommet 9 thermally expands due to the heat received from theexhaust pipe or the exhaust gas or expands at the rear side of the gassensor 200, the groove 93 of the grommet 9 is not hooked by the arm 120.As a result, the groove 93 of the grommet 9 does not expand with adifferent ratio from other regions (for example, the four regions thatconstitute the rear end surface 99), and it is thus possible to suppressthe generation of cracks in the groove 93 of the grommet 9.

Also, since a plurality of arms 120 is used, even though one arm 120 isdistorted, the other arms 120 lessen the distortion, and thus theprotection portion 110 may securely cover the atmosphere communicationhole 91 of the grommet 9 from the rear side of the outer tube 103. Inaddition, in the case where a plurality of arms 120 is used, since thearms 120 are respectively disposed in the plurality of grooves 93provided in the grommet 9, it is possible to reliably prevent theprotection portion 110 or the arms 120 from rotating in acircumferential direction of the gas sensor 200, and it is also possibleto prevent the lead wire 18 from being damaged due to contact with theprotection portion 110 or the arm 120.

Next, one example of a method for producing the gas sensor 200 isdescribed in the following sequence.

Also, though the method for producing the gas sensor 200 according tothe second embodiment is performed using the mounting jig 400 similarlyto the method for producing the gas sensor 1 according to the firstembodiment, the outer tube 103 is not held by the mounting jig 400,unlike the first embodiment, but the protection unit 100 is held by themounting jig 400. Hereinafter, the processes identical to those of themethod for producing the gas sensor 1 according to the first embodimentare not described in detail here.

First, the sensor element 6 is held to the metal shell 5, and theprotector 4 is united thereto by welding, thereby producing anintermediary body.

Meanwhile, core wires of lead wires 18 of the four connection terminals19 made of conductive plates are fixed by crimping, among which twoconnection terminals 19 are connected to the electrode 71 of the heater7. Along with receiving the connection terminals 19 and the heater 7 inthe separator 8, the lead wires 18 are inserted into the separator 8 andthe grommet 9. Also, the separator 8 and the grommet 9 into which thelead wires 18 are inserted and connected are disposed in the outer tube103.

After that, the holding bracket 85 is inserted between the outer tube103 and the separator 8 to crimp the outer tube 103 so that theseparator 8 is held by the outer tube 103. Also, the rear end 138 of theouter tube 103 is crimped so that the grommet 9 is fixed to the outertube 103, and the front end 131 of the outer tube 103 is engaged withthe rear end engagement portion 58 of the metal shell 5. Also, theperiphery of the front end 131 is crimped, and laser welding is appliedthereto.

Then, the holding process, the lead wire holding process, the disposingprocess, and the shifting process are executed in order. Also, in themethod for producing the gas sensor 1 of the first embodiment, theattachment member 400 is integrally held to the outer tube 3 during theholding process, the outer tube 3 integrated with the attachment member400 is disposed to reach the rear end of the grommet 9 during thedisposing process, and the outer tube 3 is pressed in the mountingdirection along the axis O during the shifting process.

In contrast, in the method for producing the gas sensor 200 of thesecond embodiment, the attachment member 400 is integrally held to theprotection unit 100 during the holding process, the protection unit 100integrated with the attachment member 400 is disposed to reach the rearend of the grommet 9 during the disposing process, and the protectionunit 100 is pressed in the mounting direction along the axis O duringthe shifting process. Then, the gas sensor 200 is completely produced.

In addition, the configurations in the above embodiments are justexamples, and various modifications can be made thereto.

In addition, though the first and second embodiments illustrate that thenumber of arms 33 and 120 supporting the protection portion 34 and 110is four or two, it is also possible for one arm to support theprotection portion. The number of arms may also be three, five, or more.Also, the number of grooves 93 of the grommet 9 may also be increased ordecreased depending on the number of arms, and the number of grooves 93may be greater than the number of arms.

In addition, though the protection unit 100 is mechanically united tothe outer tube 103 in the second embodiment, the invention is notlimited thereto, and it is possible to fix the protection unit 100 tothe outer tube 103 by crimping the protection unit 100 in accordancewith the crimping unit 135 of the outer tube 103.

Also, although the sensor element 6 is configured as a lower cylinder inthe gas sensors 1 and 200 according to the first and second embodiments,the invention is not limited thereto, and the sensor element 6 may havea plate shape.

It should further be apparent to those skilled in the art that variouschanges in form and detail of the invention as shown and described abovemay be made. It is intended that such changes be included within thespirit and scope of the claims appended hereto.

This application claims priority from Japanese Patent Application No.2010-085762, filed on Apr. 2, 2010, the disclosure of which isincorporated herein by reference in its entirety.

What is claimed is:
 1. A gas sensor, comprising: a sensor elementextending in an axial direction and having a detection portion fordetecting gas to be detected at a front end thereof; a metal shell thatsurrounds a periphery of the sensor element in a radial direction whileallowing the detection portion to protrude from a front end thereof; acylindrical outer tube disposed at a rear side of the metal shell andhaving a front end fixed to the metal shell; and a seal member disposedin the outer tube, the seal member including: a lead wire insert holeinto which a lead wire for extracting a detection signal of the detectoris inserted, the lead wire insert hole extending in an axial directionthereof, and an atmosphere communication hole allowing atmosphericcommunication between an inside and an outside of the outer tube througha filter member having air ventilation and waterproofing properties, theatmosphere communication hole extending in an axial direction thereof,wherein the gas sensor further includes: a protection portion thatprotects the filter member by covering the atmosphere communication holeof the seal member from a rear end of the gas sensor in the axialdirection, the protection portion having a protrusion which protrudestoward a rear side of the gas sensor, and has an opening smaller than anopening of the atmosphere communication hole, and wherein the protrusionis disposed entirely to the front of a rear end surface of the sealmember.
 2. The gas sensor according to claim 1, further comprising anarm extending from the protection portion in the radial direction,wherein the arm and the protection portion are integrally formed withthe outer tube.
 3. The gas sensor according to claim 2, wherein the sealmember is held in the outer tube by crimping the outer tube to an innerside thereof in the radial direction.
 4. The gas sensor according toclaim 1, wherein the gas sensor includes a protection unit having an armextending from the protection portion in the radial direction and acylindrical portion connected to the arm and covering the periphery ofthe outer tube, and wherein the cylindrical portion is mechanicallyfixed to the outer tube so that the protection unit is coupled to theouter tube.
 5. The gas sensor according to claim 2, wherein the sealmember has a groove extending outwards in a radial direction at a rearend-facing surface of the seal member from the atmosphere communicationhole while circumventing the lead wire insert hole, the groove having acutout toward the front end of the seal member, and wherein the arm isat least partially disposed in the groove of the seal member.
 6. The gassensor according to claim 5, wherein a plurality of grooves extendsoutwards in the radial direction at the rear end surface of the sealmember from the atmosphere communication hole while circumventing thelead wire insert hole, and wherein a plurality of arms is disposed inthe grooves of the seal member.